1. Field of the Invention
The present invention relates to devices for observing the interior contents of a vessel, and more particularly to an illuminating and viewing unit having a plurality of isolated, individually fused ports for improved illumination and viewing of the interior contents of a vessel.
2. Description of the Related Art
It is known to use various devices for direct or remote viewing of the interior of a pressure vessel, reaction vessel, or the like. A simple device for this purpose is a transparent viewing window provided in a wall of the vessel. By looking through this window, an operator can observe liquid levels, color changes, and other visually determinable factors taking place within the vessel. Several of these viewing windows are disclosed in U.S. Pat. Nos. 2,744,487; 3,299,851; 3,837,226; and 4,245,566. One problem associated with these viewing windows is that a lack of illumination within the vessel hinders observation of the vessel contents. Another serious drawback to the use of these viewing windows is the possibility that the window could fail or rupture, especially when subjected to high pressures and/or high temperatures over time. Personnel using or in the vicinity of such a window could be seriously injured if the window fails to withstand internal pressure generated within the vessel.
To overcome the problem of illumination, Thomas Canty invented a light pipe device as described in U.S. Pat. No. 4,746,178 for illuminating the interior of a pressure vessel. The device comprises a housing containing a fiber optic rod running from an external light source to a fused glass, laminated barrier disc. The unit is securely mounted on the vessel apart from a separate viewing window, with the barrier disc being arranged adjacent the interior of the vessel, whereby source light is transmitted to illuminate the vessel contents. Although this advancement significantly helps with viewing, it requires another separate aperture through the vessel wall for illumination in addition to that provided for viewing.
With regard to solving the above-mentioned safety concerns, U.S. Pat. No. 4,809,862 to Canty provides a safety viewing window comprising a transparent disc fused to a metal frame, and a laminated coating on the fused disc and frame to provide a corrosion resistant viewing window. This design has gained widespread acceptance for xe2x80x9cin personxe2x80x9d visual observation purposes, however it does not address the need for a camera observation unit that would enable a process to be monitored from a remote location and allow images of the process to be recorded.
Inspection units having camera means are taught in U.S. Pat. Nos. 4,965,601 and 4,977,418, also to Canty. In the former patent, a camera unit for high pressure/temperature applications comprises a CCD camera threadably connected to a fixed lens through a lens fitting. The lens fitting is fixed within a threaded attachment plug which mates with a threaded aperture in a vessel. A fused lens is provided at the front of the attachment plug, and is preferably overcoated with a protective laminate. The latter patent discloses a camera viewing unit including a CCTV camera mounted within a hermetically-sealed housing for axially directed adjustment relative to a fixed lens. A fused lens laminated with a protective overcoating is provided at the front of the housing. The camera units of U.S. Pat. Nos. 4,965,601 and 4,977,418 offer a means for safely monitoring vessel contents from a remote location with recording and playback capabilities. However, as with the simple viewing windows of the prior art, the crucial problem of illumination was treated separately, such that illumination and viewing were directed along different axes and optimum viewing could not be achieved.
Subsequently, illumination means and camera viewing means were combined in the same unit according to U.S. Pat. No. 5,230,556 to Canty et al. The described lighting and viewing unit includes a hermetically-sealed housing having a front fused glass window overcoated with a protective laminate, optical fibers extending from an external light source through the housing to the fused glass window, and a camera mounted within the housing with a camera lens fixed closely adjacent the fused glass window. A problem recognized in the development of this combined illumination/viewing unit involves washout due to internal reflection of illumination light by the fused glass window and/or the protective laminate back toward the camera lens. This problem is particularly noticeable with respect to wide-angle illumination and viewing arrangements involving significantly divergent rays. The reflected light causes the camera shutter to close down, resulting in an image of the vessel interior that is much dimmer than it may well be. This can compromise the image quality to the point where any internal vessel details are not visible.
The ""556 patent offers two ways of alleviating this problem. First, at column 8, lines 40-46, it suggests separating the optical fibers from the camera lens by a distance sufficient to minimize the amount of internally reflected light reaching the camera lens. Separation ensures that only higher order reflections, which have much less effect on the detected image, are introduced into the camera lens. This approach introduces limitations to the system because as the overall surface area of the front window is increased to accommodate greater spacing, the pressure rating of the unit decreases. Also, a distance between the illuminating optical fibers and the camera lens that is sufficient for one level of illumination light flux may not be sufficient for an increased level of illumination light flux. Ultimately, restrictions on viewing angle of the camera lens, pressure rating of the unit, and/or the vessel aperture size into which the unit fits must be accepted.
A second solution to the problem of reflection washout is discussed at column 8, lines 52-65. This approach involves providing an opaque ring embedded within the fused glass window and directing the optical fibers outside the ring and the camera lens inside the ring. Although suitable for many applications, this type of unit is limited in pressure rating because it relies on a single large fused glass window. Moreover, the thickness and optical nature of the window and laminate encountered by the illuminating light is necessarily the same as that encountered by light passing from the interior of the vessel to the camera lens, a restriction which may be undesirable in certain applications. Finally, the ring restricts wide-angle illuminating patterns and wide-angle viewing.
It is therefore an object of the present invention to provide a combined illuminating and viewing unit for pressure vessels wherein a camera or other radiation detector of the unit is free of washout problems due to internally reflected illuminating radiation.
It is another object of the present invention to provide an illuminating and viewing unit wherein illuminating radiation passes through one or more illumination ports that are independent in thickness, size, shape, and transmissive nature from a detection port through which detectable radiation passes to a camera lens.
It is a further object of the present invention to provide an illuminating and viewing unit that is suitable for wide-angle illumination of vessel contents.
It is a further object of the present invention to provide an illuminating and viewing unit that is suitable for wide-angle detection of radiation coming from the interior of a vessel.
It is a further object of the present invention to provide an illuminating and viewing unit that allows for significantly higher pressure retention capability when installed into a pressure retaining vessel.
It is a further object of the present invention to provide an illuminating and viewing unit that, due to reduction in port size and higher window strength, exhibits a greater resistance to thermal shock failure accompanied by loss in pressure retention ability of the vessel.
It is a further object of the present invention to provide an illuminating and viewing unit that fits in a smaller vessel aperture than previously obtainable without deleterious effect on the detected image.
These and other objects are realized in an illuminating and viewing unit of the present invention. In a preferred embodiment, the illuminating and viewing unit generally comprises a hermetically-sealed housing containing at least one radiation guide, such as a plurality of optical fibers running from an external or internal light source, and a radiation detector, such as a CCD camera. In accordance with the present invention, one or more illumination ports are individually fused within a radiation non-transmitting front wall of the housing that faces the vessel interior, and a detection port is also individually fused within the front wall. The illumination ports transmit source radiation carried by the radiation guides to the vessel interior, and the detection port transmits detectable radiation from the interior of the vessel along a detection path leading to the radiation detector. Because the illumination and detection ports are individually fused within the front wall of the unit housing, problems associated with source radiation being internally reflected into the detection path are prevented. Thus, the present invention greatly improves wide-angle illumination and wide-angle viewing capabilities relative to illuminating and viewing units of the prior art.
Moreover, this improvement is achieved without restricting pressure rating and size selection of the unit.